Question: Before the previous stop there were 84 people riding on a train. 66 people ended up getting off at the stop. How many people are riding the train now?
Solution: The number riding the train now is the difference between the number who were riding and the number who got off at the previous stop. The difference is $84 - 66$ people on the train. $84 - 66 = 18$ people are on the train.